Selective electron-phonon coupling strength from nonequilibrium optical spectroscopy: The case of MgB2

Year: 2026

Authors: Mor S., Boschini F., Razzoli E., Zonno M., Michiardi M., Levy G., Zhigadlo N.D., Canfield P.C., Cerullo G., Damascelli A., Giannetti C., Dal Conte S.

Autors Affiliation: Univ Cattolica Sacro Cuore, I LAMP Interdisciplinary Labs Adv Mat Phys, Via Garzetta 48, I-25133 Brescia, Italy; Univ Cattolica Sacro Cuore, Dept Math & Phys, Via Garzetta 48, I-25133 Brescia, Italy; Inst Natl Rech Sci Energie Mat Telecommun Varennes, Quebec City, PQ J3X 1S2, Canada; Univ British Columbia, Dept Phys & Astron, Vancouver, BC V6T 1Z1, Canada; Univ British Columbia, Quantum Matter Inst, Vancouver, BC V6T 1Z4, Canada; Synchrotron SOLEIL, F-91192 St Aubin, France; Swiss Fed Inst Technol, Lab Solid State Phys, CH-8093 Zurich, Switzerland; CrystMat Co, CH-8037 Zurich, Switzerland; Iowa State Univ, Ames Lab, US DOE, Ames, IA 50011 USA; Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA; Politecn Milan, Dipartimento Fis, Piazza L Vinci 32, I-20133 Milan, Italy; IFN CNR, Piazza L Vinci 32, I-20133 Milan, Italy; CNR, INO Natl Inst Opt, Via Branze 45, I-25133 Brescia, Italy.

Abstract: The coupling between quasiparticles and bosonic excitations rules the energy transfer pathways in condensed matter systems. The possibility of inferring the strength of specific coupling channels from their characteristic timescales measured in nonequilibrium experiments is still an open question. Here, we investigate MgB2, in which conventional superconductivity at temperatures as high as 39 K is mediated by the strong coupling between the conduction electrons and the E-2g phonon mode. By means of broadband time-resolved optical spectroscopy, we show that this selective electron-phonon coupling dictates the nonequilibrium optical response of MgB2 at early times (<100fs) after photoexcitation. Furthermore, based on an effective temperature model analysis, we estimate its contribution to the total electron-boson coupling function extracted from complementary equilibrium spectroscopy approaches, namely, optical reflectivity and angle-resolved photoemission spectroscopy. The coupling strength with the E-2g phonon modes is thus estimated to be lambda similar or equal to 0.56, which is approximately half of the total coupling constant, in agreement with ab initio calculations from the literature. As a benchmark, broadband time-resolved optical spectroscopy is performed also on the isostructural and nonsuperconducting compound AlB2, showing that the nonequilibrium optical response relaxes on a slower timescale due to the lack of strongly coupled phonon modes. Our findings demonstrate the possibility to resolve and quantify selective electron-phonon coupling from nonequilibrium optical spectroscopy. Journal/Review: PHYSICAL REVIEW B

Volume: 113 (6)      Pages from: 64514-1  to: 64514-11

More Information: The work at UBC was undertaken thanks in part to funding from the Max Planck-UBC-UTokyo Centre for Quan-tum Materials and the Canada First Research Excellence Fund, Quantum Materials and Future Technologies Program. This project is also funded by the Canada Foundation for Innovation (CFI) ; the British Columbia Knowledge Develop-ment Fund (BCKDF) ; the Natural Sciences and Engineering Research Council of Canada (NSERC) ; the Department of National Defence (DND) ; the Fonds de recherche du Quebec-Nature et Technologies (FRQNT) ; the Ministere de l’Economie, de l’Innovation et de l’Energie-Quebec; the Canada Research Chair Program (A.D. and F.B.) ; and the CI-FAR Quantum Materials Program (A.D.) . C.G. acknowledges financial support from MIUR through the PRIN 2017 (Prot. 20172H2SC4 005) and PRIN 2020 (Prot. 2020JLZ52N 003) programs and from the European Union-Next Generation EU through the MURPRIN2022 (Prot. 20228YCYY7) program. C.G. and A.D. received support for collaborative research from the Peter Wall Institute for Advances Studies. G.C. and S.D.C. acknowledge support from the European Union’s Next Generation EU Programme with the I-PHOQS Infrastructure 423 (IR0000016, ID D2B8D520, CUP B53C22001750006) Integrated infrastructure initiative in Photonic and Quantum Sciences. Work done at Ames National Laborator y (PCC- crystal growth) was supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.
KeyWords: Normal-state; Temperature; Heat; Electrodynamics; Superconductor; Origin
DOI: 10.1103/25zv-zv94